1. Field of the Invention
The present invention is generally in the field of electronic circuits and interconnections. More particularly, the invention is in the field of communications circuits and interconnections.
2. Background Art
Electronic devices, such as Ethernet devices and other types of communications devices, can communicate via communications media, such as Ethernet cables. A communications medium, such as an Ethernet cable, can include, for example, two or more differential pairs of wires coupled to corresponding pins on a connector, such as an RJ45 plug, which can be connected to a corresponding receptacle on an electronic device, such as an Ethernet device. However, a communications medium, such as an Ethernet cable, is susceptible to common-mode (CM) noise, which can be coupled to the communications medium from nearby electronic devices, such as radio frequency (RF) transmitters, cell phones, lightning discharges, electrostatic discharges, and the like. A portion of the CM noise on the communications medium can be converted by pins in the connector to differential-mode (DM) noise, which can undesirably affect device operation. Conversely, a portion of a DM signal generated by the electronic device can be converted by the connector pins to CM noise, which can undesirably increase device EMI emission.
In a conventional approach, CM noise suppression components, such as CM chokes and transformers, can be place on a circuit board in the electronic device, such as an Ethernet device, and/or integrated into a receptacle on the device to reduce CM noise. However, CM noise suppression components that are located within the electronic device cannot attenuate DM noise that has been coupled into the device from a connector attached to the communications medium, where the DM noise has been converted from CM noise on the communications medium by the connector pins.
In another conventional approach, CM noise coupling between the communications medium, such as an Ethernet cable, and the electronic device can be reduced by placing a clamp-on ferrite choke on the communications medium close to an attached connector that is plugged into the device receptacle. However, to significantly reduce CM noise on the communications medium, a large-size clamp-on ferrite choke is required, which is undesirable. Also, this approach is impractical where a large number of connectors are adjacent to one another, as required in, for example, a multi-port communications device, such as an Ethernet switch.